1. Field of the Invention
This invention concerns detergent compositions comprising low levels of phosphate builder.
2. Description of the Prior Art
Detergent compositions intended primarily for laundering heavily soiled fabrics generally contain two essential components: a builder and a detergent. The primary purpose of the builder is to tie-up hardness mineral ions such as calcium and magnesium that are commonly found in tap water and soiled fabrics. The tie-up of such ions can be accomplished by the inclusion in the detergent composition of a sequestering-type builder, e.g. sodium tripolyphosphate, or a precipitating-type builder, e.g. sodium carbonate. Regardless of which type of builder is used, the effect is the same; the hardness mineral ions are effectively "removed" from the wash solution. In the absence of a builder, the hardness mineral ions react with the detergent and the soil. Such a reaction should be avoided because it renders the detergent less effective for its cleaning function as well as forming an undesirable insoluble product which may deposit itself on the fabrics being washed.
Common builders used throughout the detergent industry have been the phosphates, in particular sodium tripolyphosphate. This builder, when used in a sufficient quantity, effectively sequesters hardness mineral ions in a wash solution and performs certain other beneficial secondary functions. For instance, it is very effective in removing clay soil, it aids in keeping soil removed from the fabrics in solution and off the cleaned fabrics, and it buffers the wash solution pH at a desired alkaline value. The amount of phosphate needed in a detergent composition is in part determined by the hardness of the wash water to be used. For example, some areas of the world have quite hard water which contains about 2.5 mmoles of calcium per liter. In these areas, a relatively large amount of builder has to be used to tie-up all the hardness mineral ions. Because a detergent composition is generally manufactured to be sold over a wide area, it is usually formulated so as to be effective in both hard and soft water areas. Detergent compositions often contain as much as 65% sodium tripolyphosphate by weight and seldom less than 25%. Such high phosphate content compositions when used at the recommended levels give a builder to hardness mineral ion ratio above 1 and are considered to be fully built-detergent compositions.
Phosphates are proven builders which are satisfactory in many respects. However, they have come under recent criticism for their possible adverse effect on the environment. Because phosphates are a nutrient, there are some who fear that their discharge into natural waterways will cause an excessive growth of plant organisms. This plant life can consume excessive amounts of oxygen found in the water; fish are then deprived of this necessary substance. Because of the concern over the possible adverse effect phosphates have on the environment, efforts have been made to reduce or replace the phosphates in detergent compositions. Such efforts have been difficult due to the many functions the phosphates perform in a detergent composition. Thus, the complete replacement of the phosphate builder with another safe (both environmentally and humanly safe) builder without suffering a cleaning performance drop has not been completely satisfactorily accomplished. Merely reducing the phosphate content of the detergent composition has met with predictable unacceptability in terms of cleaning performance.
Some prior art methods of formulating zero or low phosphate detergent compositions have involved using water-soluble organic detergents which are insensitive to hardness mineral ions found in normal laundering solutions. (See for example U.S. Pat. Nos. 2,543,744, 2,744,874, 2,875,153, 3,520,925, 3,583,091 and 3,619,119.) While some of these compositions are satisfactory, there is a continuing need for a low phosphate detergent composition possessing satisfactory cleaning ability.